Polyaspartic acids have utility as calcium carbonate and calcium phosphate inhibitors. Their biodegradability makes them particularly valuable from the point of view of environmental acceptability and waste disposal.
Anhydropolyaspartic acids (i.e., polysuccinimides) are the anhydrous forms of polyaspartic acids.
Thermal condensation of aspartic acid to produce polyaspartic acid is taught by Etsuo Kokufuta, et al., "Temperature Effect on the Molecular Weight and the Optical Purity of Anhydropolyaspartic Acid Prepared by Thermal Polycondensation," Bulletin of the Chemical Society Of Japan 51(5):1555-1556 (1978). Kokufuta et al. teach that the molecular weight of the polyaspartic acid produced by this method increases with increased reaction temperature. Moreover, the suggested maximum percent conversion of the aspartic acid to anhydropolyaspartic acid is no more than 68% using oil bath temperatures of between 325.degree. F. and 425.degree. F.
A more recent work by Brenda J. Little et al., "Corrosion Inhibition By Thermal Polyaspartate" Surface Reactive Peptides and Polymers, pp 263-279, American Chemistry Society Symposium Series 444(1990), cites Kokufuta et al. Oil bath temperatures of 374.degree. F. were reportedly used to produce anhydropolyaspartic acid from powdered aspartic acid over a period of 24 to 96 hours. The reported results were no better than those reported by Kokufuta et al., however.